// Copyright 2015-2017 Parity Technologies (UK) Ltd.
// This file is part of Parity.

// Parity is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Parity is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Parity.  If not, see <http://www.gnu.org/licenses/>.

use migration::SimpleMigration;

/// This migration reduces the sizes of keys and moves `ExtrasIndex` byte from back to the front.
pub struct ToV6;

impl ToV6 {
	fn migrate_old_key(&self, old_key: Vec<u8>, index: u8, len: usize) -> Vec<u8> {
		let mut result = vec![];
		result.reserve(len);
		unsafe {
			result.set_len(len);
		}
		result[0] = index;
		let old_key_start = 33 - len;
		result[1..].clone_from_slice(&old_key[old_key_start..32]);
		result
	}
}

impl SimpleMigration for ToV6 {

	fn columns(&self) -> Option<u32> { None }

	fn version(&self) -> u32 { 6 }

	fn simple_migrate(&mut self, mut key: Vec<u8>, value: Vec<u8>) -> Option<(Vec<u8>, Vec<u8>)> {
		//// at this version all extras keys are 33 bytes long.
		if key.len() == 33 {
			// block details key changes:
			// - index is moved to the front
			if key[32] == 0 {
				return Some((self.migrate_old_key(key, 0, 33), value));
			}

			// block hash key changes:
			// - key is shorter 33 -> 5 bytes
			// - index is moved to the front
			if key[32] == 1 {
				return Some((self.migrate_old_key(key, 1, 5), value));
			}

			// transaction addresses changes:
			// - index is moved to the front
			if key[32] == 2 {
				return Some((self.migrate_old_key(key, 2, 33), value));
			}

			// block log blooms are removed
			if key[32] == 3 {
				return None;
			}

			// blocks blooms key changes:
			// - key is shorter 33 -> 6 bytes
			// - index is moved to the front
			// - index is changed 4 -> 3
			if key[32] == 4 {
				key.reverse();
				// i have no idea why it was reversed
				let reverse = key;
				let result = vec![
					// new extras index is 3
					3,
					// 9th (+ prefix) byte was the level. Now it's second.
					reverse[9],
					reverse[4],
					reverse[3],
					reverse[2],
					reverse[1],
				];

				return Some((result, value));
			}

			// blocks receipts key changes:
			// - index is moved to the front
			// - index is changed 5 -> 4
			if key[32] == 5 {
				return Some((self.migrate_old_key(key, 4, 33), value));
			}
		}

		Some((key, value))
	}
}